The present invention relates to a caisson for converting the sea wave motion into a form which is more suited for conversion.
A caisson like that of the present invention, may be used for the construction of a plant, comprising one or more caissons, said plant having the structure of a caisson breakwater and being suited to be built in a dry dock, and hence towed and sunk.
The resonance effect for the absorption of wave energy has been exploited only for solid floating bodies, and no device exists at present which exploits the resonance of a water mass.
Moreover, the traditional absorbers require a substantially continuous regulation, which is performed at intervals of only a few seconds, and this circumstance noticeably complicates the operation of wave energy absorption devices. An object of the present invention is to realize a device in the form of a caisson used to convert the energy of sea waves into hydraulic energy which can be directly exploited, and wherein the adjustment of operative conditions of the caisson can occur at intervals of about ten to twenty minutes, depending on the variation of the xe2x80x9csea statexe2x80x9d (a substantially stationary wave condition). Since the sea state has a duration of at least ten to twenty minutes, the adjustment will be performed at variable intervals of ten to twenty minutes.
A specific object of the present invention is that of realizing a caisson, or a plant comprising several caissons, which is capable or absorbing a high share of the wave energy passing above it, by producing very high pressure fluctuations inside it, and also high current speeds. The amplitude of the pressure fluctuations inside the caisson can exceed, by an order of magnitude, the corresponding amplitude of the surface waves.
Finally, a further object of the present invention is the use of special turbines with vertical axis, allowing the conversion into mechanical rotational energy, of the portion of wave energy which has been already converted into a suitable form by means of the caisson of the present invention.
The objects of the invention are obtained by means of a caisson, which is characterized in that it comprises internally at least an air pocket, and at least a vertical duct which extends transversally along the whole portion of the caisson where the air pocket is present, and wherein the lower portion of the caisson is filled with water, and the vertical duct extends upwardly* passing through the upper wall of the caisson and communicates with the outside of the caisson, without reaching with its upper aperture the sea surface, whereas at the lower end it does not reach the base of the caisson, defining at this location a lower aperture; the height of the air pocket, from the ceiling of the caisson, toward$ its base, being adjusted through air feeding and air discharge means to the outside, thereby obtaining the resonance condition in which the period of pressure fluctuations at the upper aperture of the vertical duct, or at a point below the sea surface, but located outside the caisson, is equal to the period of pressure fluctuations of the air pocket or to the period of pressure fluctuations at any point located inside the caisson.
Particular embodiments of the present invention are defined in the dependent claims.